Overview Nitrogen fertilizer will continue to be indispensible for meeting global food, feed, and fiber needs. Voroneyand Derry (2008) estimated that 340 million Mg yr-1 N is fixed by natural means, including lightning and biological N fixation, and 105 million Mg yr-1 is fixed by human activities, including burning of fossil fuels and N fertilizer production, with N fixation by human activities expected to continue to increase. Townsend and Howarth (2010) estimated the amount of N fixed by human activities to be about 180 million Mg yr-1, with most used as mineral fertilizer. Fertilizer N production has important environmental implications with an average of ~2.55 kg CO2 emitted per kg fertilizer N fixed and transported (Liska et al., 2009). Th e amount of N applied is associated with emission of N2O (IPCC–OECD, 1997) and N accumulation in sensitive aquatic, marine, and terrestrial ecosystems (Groffman, 2008; Malakoff , 1998). Th e challenge is to produce more grain to meet growing global needs with high NUE.

Conclusions Across diverse production environments, high corn yields can be achieved with efficient use of soil and applied N and without high risk of NO3 -N leaching to groundwater. With excellent farm management, recovery of applied fertilizer-N in high-yielding corn fields of Nebraska was well above 60 to 70% at the economically optimal nitrogen rate (EONR), resulting in low residual soil nitrate nitrogen (RSN) levels. Agronomic efficiency and crop partial factor productivity (PFP), the Nitrogen use efficiency (NUE) components most closely related to profitability of production, can also be high at EONR. Less preplant and more in-season N application may be especially important for drybean (CD) which had low recovery efficiency (RE) and much postharvest RSN compared with corn (CC) and soybean (CS). The levels of NUE achieved in our study for CC and CS far exceed current national or regional means, demonstrating the potential for high NUE with high yield corn production. Further NUE efficiency may be gained through more accurate in-season N application such as with use of the presidedress NO3 test (Andraski and Bundy, 2002) and spatial variation in N rate in response to variation in crop need, such as through use of reflectance sensors (Scharf and Lory, 2009; Barker and Sawyer, 2010; Roberts et al., 2010).

Recent studies have related large-scale dune activity in the Nebraska Sandhills and elsewhere on the western Great Plains to prehistoric megadroughts. At the eastern margin of the Great Plains, however, little or no effort has been expended toward identifying the impacts and severity of these climatic events. The eastern margin of the Great Plains should be of particular interest in paleclimate studies because it represents an important biogeographic boundary that may have shifted over time. In dunes around the present confluence of the Loup and Platte Rivers near Duncan, Nebraska, optical dating contrains, for the first time, the chronology of dune activity in the central-eastern margin of the Great Plains. A total of 17 optical age estimates taken from dune sediments clearly indicate two significant periods of dune activation at 5,100 to 3,500 years ago and 850-500 years ago. These reconstructed time intervals overlap both periods of large-scale dune activity in the Nebraska Sandhills and ancient droughts identified from other paleoclimate proxy records on the western Great Plains. The agreement between results from the eastern margin of the Great Plains and data from farther west indicate that megadroughts were truly regional in their effect. In order to further test a hypothesis of geographically-widespread megadrought effects, future work will date other dune deposits in eastern Nebraska from sites along the Loup and Elkhorn Rivers, as well as dunes in east-central Kansas and western Iowa.

Each day University of Nebraska Extension makes a difference in the lives of adults and youth. The faculty and staff in the Southeast Research and Extension Center and the 28 County Offices work to bring relevant researched based information to people in communities, towns and urban centers. Our efforts rely increasingly on partnerships with government agencies, business, industry, schools and community organizations. Working together with our partners Extension strives to strengthen the social, economic and environmental base of Nebraska's communities. Our programs must be ever-changing as Extension listens and responds to issues as they evolve. The Southeast Research and Extension District is unique because it serves both urban and rural communities Nebraska. The faculty and staff are committed to bringing the resources of the University and its research based information to the individuals and communities of Southeast Nebraska.

Project Support

Varies according to program and project - for more information see http://www.southeast.unl.edu/

The hydrologic properties of channel sediments have an important role in controlling hydrologic process in streams. This study focused on the water exchange between a stream and an aquifer induced by groundwater withdrawal, with the purpose of investigating the interbedded feature of channel sediments and to evaluate its effects on the calculation of streamflow depletion. Field work was conducted at nine study sites between Kearney and Columbus during the summers of 2005 and 2006. Direct-push techniques were used to produce electrical conductivity logs and to collect sediment cores. Permeameter tests were conducted on the sediment cores. Stream-aquifer simulation models were used to evaluate streamflow depletion for various types of channel sediments.

Sediment core samples were categorized into four groups:

sand and gravel,

sand and gravel with interbedded silt and clay layers,

fine sand with silt or clay layers, and

silt and clay with some sand and gravel.

In general coarse sediments occur in the western part of the study area, and the amount of fine sand, silt and clay increases eastward along the river. However, the sediments in the top two meters are about the same for all the sites, consisting mainly of sand and gravel.

Investigation of Stream-Aquifer Hydrologic Relationship for Clear Creek in Polk and Butler Counties

Other(s)

Weihong Dong, Jilin University; Zhaowei Wang, School of Natural Resources; Gengxin Ou, School of Natural Resources; Can Liu, School of Natural Resources, can.liu1989@huskers.unl.edu

Description

Vertical hydraulic conductivities (Kv) of both streambed and point bars can influence water and solute exchange between streams and surrounding groundwater systems. The sediments in point bars are relatively young compared to the older sediments in the adjacent aquifers but slightly older compared to submerged streambeds. Thus, the permeability in point bar sediments can be different not only from regional aquifer but also from modern streambed. However, there is a lack of detailed studies that document spatial variability of vertical hydraulic conductivity in point bars of meandering streams. In this study, the authors proposed an in situ permeameter test method to measure vertical hydraulic conductivity of the two point bars in Clear Creek, Nebraska, USA. We compared the Kv values in streambed and adjacent point bars through 45 test locations in the two point bars and 51 test locations in the streambed.

The Kv values in the point bars were lower than those in the streambed. Kruskal–Wallis test confirmed that the Kv values from the point bars and from the channel came from two statistically different populations. Within a point bar, the Kv values were higher along the point bar edges than those from inner point bars. Grain size analysis indicated that slightly more silt and clay particles existed in sediments from inner point bars, compared to that from streambed and from locations near the point bar edges. While point bars are the deposits of the adjacent channel, the comparison of two groups of Kv values suggests that post-depositional processes had an effect on the evolution of Kv from channel to point bars in fluvial deposits.

We believed that the transport of fine particles and the gas ebullition in this gaining stream had significant effects on the distribution of Kv values in a streambed-point bar system. With the ageing of deposition in a floodplain, the permeability of point bar sediments can likely decrease due to reduced effects of the upward flow and gas ebullition.

Over extraction of groundwater near a stream can lower stream stage and induce streamflow depletion when the stream and aquifer are hydrologically connected. The Little Blue River Basin is an area of intensive groundwater development for irrigation, and the streamflow depletion in this basin was determined by an analog model (Emery, 1966). However, the post audit of the model (Alley and Emery, 1986) suggested that the decline of water-levels was overestimated and streamflow depletion was underestimated. Therefore, it is necessary to re-evaluate stream-aquifer interactions in the basin. In this study, an area is chosen for this analysis from the basin and three main streams -- the Little Blue River, Big Sandy Creek, and Spring Creek are included. Channel sediments and structures play an important role in determining stream-aquifer interactions. Firstly, field and laboratory methods including geoprobe logging and permeameter tests are utilized to investigate the channel deposits in the three main streams in the Little Blue River Basin. Results show that channels have low hydraulic-permeable layers which reduce their hydraulic connections to the adjacent aquifers. Secondly, a groundwater flow model is constructed to identify the hydraulic properties of the aquifer and evaluate streamflow depletion under groundwater withdrawals in the study area. Modeling results indicate that streamflow depletion is very low and aquifer storage loss is the main source of groundwater pumpage.

Groundwater Flow Model for the Lower Platte North Natural Resources District

Other(s)

Cheng Cheng, School of Natural Resources

Description

Compared to other parts of Nebraska, the Platte River is wide and thus it is more challenging to characterize its hydrologic connections with the surrounding aquifers. The shallow aquifer consists of the alluvial and glacial deposits and displays strong heterogeneity. A three-dimensional groundwater flow model is developed using Visual MODFLOW to evaluate the impacts of groundwater withdrawals on the stream-aquifer system in the Lower Platte River Basin. The study area is about 65 miles by 50 miles and is located in eastern Nebraska. Two pumping tests were conducted to determine the hydraulic properties of the aquifers and aquitards, which are beneficial for model calibration. In-situ and laboratory permeameter tests of streambed sediments in the Platte River were per-formed to determine the streambed vertical hydraulic conductivity (Kv) values, which play an important role in controlling stream-aquifer interactions. The ground-water flow model integrates the geological, hydrological, precipitation, and soil information. The test-hole logs combining with the irrigation well logs were used to define the hydrostratigraphic units. The model is divided into 5 layers with 201 columns and 195 rows in each layer. The Platte River is simulated by the constant-head boundary package in MODFLOW. The model is calibrated using the groundwater level measurements of the USGS and local Natural Resources District observation wells from January 1950 to December 2004. The time interval of the calibration is divided into 660 stress periods, and each stress period consists of 10 time steps. Trial-and-error calibration is used to determine the hydraulic conductivity, specific yield, and specific storage of the aquifers and aquitards. Furthermore, the values of groundwater recharge and evapotranspiration are estimated by model calibration. After the model is well calibrated, it is used to determine the impacts of groundwater pumping over the 55 year periods on the streamflow in the Platte River.

Streambed vertical hydraulic conductivity (Kv) plays an important role in understanding and quantifying the stream-aquifer interactions. While several researchers have discussed the spatial variability of streambed horizontal hydraulic conductivity or Kv at one or several close-located sites in a river, they did not develop any statistical distribution analysis of streambed Kv at distant sites along a large river. In this paper, the statistical distribution and spatial variation of streambed Kv at 18 test sites in a 300-km reach of the Platte River in Nebraska are presented. Insitu permeameter tests using the falling-head method were carried out to calculate the streambed Kv values. Fine-grained sediments transported by two tributaries, the Loup River and the Elkhorn River, to the Platte River appear to result in lower streambed Kv values downstream of the confluences between the Platte River and the tributaries. The streambed Kv values were found to be normally distributed at nearly each test site. When the correlated Kv values were eliminated from the grid sampling plots, the remaining independent sub-datasets of streambed Kv values were still in normal distribution at each test site. Furthermore, the combined streambed Kv values upstream of the first confluence between the Platte River and the Loup River was normally distributed, which may be due to the lack of tributaries in-between and thus streambed sediments were well distributed in this reach and belonged to a single population of hydraulic conductivity values. In contrast, the combined dataset of all measurements conducted downstream of this confluence was no longer in normal distribution, presumably as a result of the mixing of different sediment sources.

Project Support

Lower Platte North Natural Resources District, Program for Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China

Visit the Nebraska Maps and More website (http://nebraskamaps.unl.edu/home.asp) to order an excellent publication that describes this project more in-depth, Bulletin 1: Eastern Nebraska Water Resources Assessment (ENWRA) Introduction to a Hydrogeological Study.

Description

Eastern Nebraska contains 70% of the state's population, but is most limited in terms of the state's groundwater supplies. The population in this region is expected to increase; thus the need for reliable water supplies is paramount. Natural resources districts (NRDs), charged with ground water management in Nebraska, seek to improve their management plans in response to growing populations, hydrologic drought, and new conjunctive management laws. Detailed mapping and characterization is necessary to delineate aquifers, assess their degree of hydrologic connection with streams and other aquifers, and better predict water quality and quantity.

In a collaborative effort between local, state, and federal agencies, the ENWRA project has been initiated to gain a clearer understanding of the region's groundwater and interconnected surface water resources. These resources can be difficult to characterize because of the complex geology created by past glaciations. Acquiring geologic and hydrologic data in the eastern, or glaciated, part of Nebraska requires the use of multiple, innovative techniques. Currently, little is known about which techniques are most effective and feasible. Once identified, the most effective and feasible tools will be used to provide data, interpretations, and models for improved water resources management.

The ENWRA group has established three pilot test sites for intensive study using a variety of investigative techniques. The goal of the initial work being done at the three pilot test sites is to determine the location, extent, and connectivity of aquifers with surface waters, with the hope of expanding these investigative techniques across other portions of eastern Nebraska. The pilot test sites are located near Oakland, Ashland, and Firth with each site exhibiting differing geologic conditions. The techniques that will be utilized in the study include: 1) helicopter electromagnetic (HEM) surveys; 2) ground-based geophysical surveys; 3) test hole drilling; and 4) geochemical analysis, just to name a few. So far HEM surveys were completed over approximately one township at each site. Other techniques were used to provide "ground truth" data to support the HEM interpretations.

The goal of this project is to quantify riparian evapotranspiration (ET) by utilzing satellite and air-borne remote sensing data on selected watersheds in the North Platte River. The results will be used to develop guidelines on riparian water use.

The goal of this project is to quantify riparian evapotranspiration (ET) by utilzing satellite and air-borne remote sensing data on selected watersheds in the North Platte River. The results will be used to develop guidelines on riparian water use.

Fate and bioavailability of steroidogenic compounds in aquatic sediment

Other(s)

Daniel Snow, School of Natural Resources, dsnow1@unl.edu; Alan Kolok, UNO School of Public Health, akolok@mail.unomaha.edu

Description

Objective: To improve understanding of the role of sediment in the environmental fate, transformation and subsequent bioavailability of steroidogenic compounds. The central hypothesis of this study is that sediment-associated steroids remain bioavailable.

Research Questions: Are sediment-associated steroids bioavailable?
How do sediment characteristics influence steroid fate?
What biologically active steroid metabolites are produced in sediment?

Remote sensing is a useful tool for providing regulatory officials with the data necessary to make decisions regarding recreational waters. In 2005, CALMIT scientists undertook a collaborative effort with the Nebraska Department of Environmental Quality aimed at developing a tool to identify lakes where blue-green algae populations are present. The overall purpose was to incorporate those affected lakes into a toxic-algae alert procedure to provide early warnings to the public about the potential danger. This project also served to promote coordination and information sharing about toxic-algae issues among local units of government, lake associations, lake owners, and the public.

Both in-situ (close-range) and remote techniques were employed to detect and quantify in real-time the algal phytoplankton pigment concentration and composition (i.e., chlorophyll-a and phycocyanin in the water column). Two criteria were used to identify lakes and reservoirs with high probability of toxic algae: 1) chlorophyll concentration above 50 mg/m3; and 2) existence of blue green algae (the phycocyanin absorption feature has been used to indicate remotely the presence of blue-green algae). These criteria were tested by analytical assessment of toxic algae and the tests were positive: when the sensor systems indicated high probability of toxins, they were found in water samples.

The Rainwater Basin is one of the most endangered wetland ecosystems in North America. This ecosystem is critical to many species including migratory waterfowl. Land use and runnoff from agriculture and cattle confinement operations are likely to be reducing the basin's health and diversity, however little information exists concerning macroinvertebrates. Twenty-two locations were assessed for water quality parameters, vegetation composition, and macroinvertebrates identified to genus. Samples were collected biweekly starting in April through July for three years. Macroinvertebrate diversity was impacted in areas with little buffer although the effects were not pronounced. Institution of a more effective vegetative buffers strip may reverse this trend to improve ecosystem quality and provide for invertebrate resources for migratory birds.

The overall goal of this project is to prioritize watershed restoration/acquisition programs in the Rainwater Basin (RWB) by examining playa wetlands’ sedimentation and water quality conditions using the Revised Universal Soil Loss Equation 2 (RUSLE2) and the fly ash technology.

Three specific tasks are included in this project:

Calculate and map the sedimentation rates and the age of deposition for all playa wetlands in RWB

Consolidate existing water quality data of the RWB playa wetlands and evaluate the key factors influencing playa wetland water quality

Assess the effects of sedimentation control practices and prioritize future watershed restoration/acquisition programs

The final products of this project include:

An atlas of wetland sedimentation maps and a risk report highlighting the areas in watersheds with the highest sedimentation rates

A geodatabase and an evaluation report on the water quality conditions of the playa wetlands in the RWB

A written assessment report for sedimentation control practices and a watershed index to prioritize future conservation/acquisition programs

The overall goal of this project is to provide wetland managers with topographically-correct 3-D wetland maps to prioritize wetland conservation efforts and assess wetland conservation design practices. This project addresses three specific tasks for the playa wetlands: 1) Establish accurate, topographically-correct, 3-D wetland maps to relate weather conditions and wetland functions; 2) Develop a measurable Restorable Wetland Index to prioritize playa wetland and drainages conservation; 3) Assess wetland conservation design practices for watershed-based wetland conservation. This research will use high-resolution Light Detections And Ranging (LiDAR) data to create next-generation wetland maps for playa wetlands. The research provides the missing link in conservation design as these data will provide accurate elevation measures to delineate watershed extent and determine the impact of individual hydrologic modifications. This project will be one of the first to integrate LiDAR data and a hydrologic modifications datasets to find the relations of current weather conditions and wetland functions. This project provides reliable, accurate wetland spatial parameters to prioritize playa wetland conservation and assess the effectiveness of existing wetland conservation design practices. The wetland conservation design tools and protocols will be examined in two pilot counties in Nebraska. The intellectual merit of the research is based on advancing knowledge linkage of wetland mapping technologies and wetland function modifications, and showing how to adapt wetland conservation designs. The outputs from this project provide practical protocols for state/regional/local wetland managers and thus ensure "no net loss" in quality and quantity of wetlands.

Reduction in range and abundance of shovelnose sturgeon Scaphirhynchus platorynchus over the past century has been primarily attributed to critical habitat loss, poor water quality, and overharvest. These declines have led to concerns about populations of this once ubiquitous sturgeon species in large rivers throughout their Mississippi River Basin-wide range. However, detailed analyses of shovelnose sturgeon populations do not exist in several potentially important portions of their range, such as the Platte River, Nebraska. Shovelnose sturgeon, for example have been documented in the Lower Platte River, Nebraska (i.e., Columbus, NE to Plattsmouth, NE), but little is known about their population dynamics. Additionally, indications that seasonal fishing pressure in the Lower Platte River may affect local abundances, growth and mortality rates, and age at maturity of shovelnose sturgeon create a need for obtaining more specific population information. Researchers have initiated a five year study of the shovelnose sturgeon population in the Lower Platte River to characterize the abundance, distribution, demography, population dynamics, and genetics of shovelnose sturgeon. For preliminary data from the first year of sampling, view the presentation via the website like below.

Catfish angling is popular throughout the United States and catfish are the most sought after fish species in the Platte River. However, catfish management in the Platte River is minimal as little is known about current populations. The objective of this study was to determine the current status of channel catfish and flathead catfish populations in the central and lower Platte River. Specifically, the study evaluated population characteristics including relative abundance, size structure, condition, age, growth and mortality.

Channel catfish are much more abundant than flathead catfish in the Platte River. The current Platte River channel catfish population appears to be average, comparable to many Nebraska and Midwestern rivers. Population characteristics displayed considerable variation along the Platte River and some longitudinal patterns were evident. Channel catfish in the central Platte River had lower relative abundances, higher condition, greater size structure, faster growth and lower mortality compared to lower Platte River channel catfish. Key factors likely influencing differences in channel catfish population characteristics are prey availability, flow modifications, habitat characteristics, tributary inflows and angler exploitation. Water manipulations from the Loup River Power Canal were also identified as a possible negative influence on lower Platte River channel catfish populations because hydropeaking is likely creating a stressful environment. However, channel catfish in the central Platte River appear to have benefited from recent high flows that likely increased productivity and food availability in the central Platte River.